1. Field of the Invention
The invention is related to the field of fuel injection pumps and in particular to a distributor fuel injection pump in which the period of fuel injection is controlled in response to an electric signal.
2. Prior Art
Distributor fuel injection pumps in which the period of fuel injection is controlled mechanically or hydraulically are well known in the art. The injector pumps disclosed by Stein in U.S. Pat. No. 4,125,104, Sosnowski et al. in U.S. Pat. No. 4,173,959 and Bailey in U.S. Pat. No. 4,200,072, are typical of these types of distributor fuel injector pumps. Recent advances in electronics have resulted in the development of electronic fuel control units which are capable of more accurately computing fuel requirements in response to one or more operational parameters of the engine. These electronic control units are capable of not only computing the required fuel quantity, but also the time at which the fuel is to be injected into the cylinder to optimize the engine's performance. Concurrent with this development has been the development of distributor injection pumps in which the fuel quantity and injection timing are electrically controlled in response to electrical signals generated by electromechanical devices as well as electronic control units. Typical examples of electrically controlled distributor fuel injection pumps are disclosed by Watson et al. in U.S. Pat. Nos. 3,779,225 and 3,859,972 and by Twaddell et al. in U.S. Pat. No. 3,880,131. In U.S. Pat. No. 3,779,225, Watson et al. discloses a distributor injection pump which requires one electrically activated solenoid valve for each output injection port. Alternatively, Watson et al. and Twaddell et al. in U.S. Pat. Nos. 3,859,972 and 3,880,131 disclose injection pumps using two electrically activated solenoid valves. One of the solenoid valves initiates the beginning of the fuel injection pulse and the second terminates the injection pulse. Both solenoid valves act to spill the high pressure injection pulse in its unenergized state.
The disclosed distributor injection pump is an improvement over the injection pumps of the prior art having a single solenoid valve controlling the injection period.